das Salzwasser
salt water
Water that has a high content of dissolved salts, as found in seas and oceans.
Beim Schwimmen im Meer habe ich aus Versehen Salzwasser geschluckt.
While swimming in the sea, I accidentally swallowed salt water.

salt water
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salt water
Water that has a high content of dissolved salts, as found in seas and oceans.
Beim Schwimmen im Meer habe ich aus Versehen Salzwasser geschluckt.
While swimming in the sea, I accidentally swallowed salt water.

The word is simply made up of 'Salz' (salt) and 'Wasser' (water). So it literally describes water that contains salt.
Das Wasser im Toten Meer ist extremes Salzwasser.
The water in the Dead Sea is extremely salty salt water.
The meaning depends on the context. If people are talking about the sea, the beach, or swimming, seawater is meant. If they are talking about cooking, recipes, or home remedies, the homemade salt solution is meant.
Die Luft am Meer riecht nach Salzwasser.
The air by the sea smells of salt water.
The salt solution is mainly used in two contexts: in cooking ('Nudeln in Salzwasser kochen' — to cook pasta in salt water) or as a home remedy for sore throats ('mit Salzwasser gurgeln' — to gargle with salt water).
Der Arzt hat mir empfohlen, bei Halsschmerzen mit Salzwasser zu gurgeln.
The doctor recommended that I gargle with salt water for my sore throat.
brine
'die Sole' and 'das Salzwasser' both mean water with dissolved salt. The difference is mainly in the concentration and typical use. 'Salzwasser' is the general term, for example for seawater or for water with salt in the kitchen. 'Sole' is usually a particularly salt-rich solution and is often used in therapeutic baths, for preservation, or against ice. The words can be confused because 'Sole' is always a type of 'Salzwasser'. But not every kind of 'Salzwasser' is called 'Sole'.

Im Urlaub schwimmt Paul jeden Morgen im Salzwasser.
On vacation, Paul swims in salt water every morning.
Im Kurort badet Maria in warmer Sole, weil das gut für ihre Haut sein soll.
At the spa town, Maria bathes in warm brine because it is supposed to be good for her skin.